Bacteria in Your Mouth Could Fuel Gut Diseases

A woman opens her mouth wide, as if in pain
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Bacteria that normally live in a person's mouth could contribute to gut diseases such as inflammatory bowel disease (IBD), ulcerative colitis and Crohn's disease, a new study in mice suggests.

The study found that, when certain strains of bacteria from the mouth make their way to the gut and settle down in the intestine, they can trigger chronic inflammation under certain circumstances.

The findings are preliminary and more research is needed to confirm the results in people. But if true, the study suggests that finding ways to target oral bacteria living in the gut could provide a new treatment for IBD and other gut diseases, the researchers said. [5 Ways Gut Bacteria Affect Your Health]

Previous studies have suggested that oral bacteria don't typically live in a healthy person's gut, because these bacteria are out-competed by other bacterial species already living in the gut. However, higher levels of oral bacteria have been found living in the guts of people with certain diseases, including IBD and colon cancer, the researchers said.

To further examine the link between oral bacteria and gut diseases, the researchers took saliva samples from patients with Crohn's disease and IBD, and transplanted the sampled bacteria into mice bred to not produce their own gut bacteria (called germ-free mice). They found that a strain of bacteria in the saliva called Klebsiella pneumoniae could inhabit the intestines of the germ-free mice and activate types of immune cells known as "T helper cells," which, in turn, can trigger an inflammatory response.

When the researchers inserted this strain of Klebsiella pneumoniae in another type of mouse with healthy or "balanced" levels of gut bacteria, K. pneumoniae couldn't establish itself in the gut. But when these mice were fed certain antibiotics, K. pneumoniae could persist in the intestine, the researchers said.

What's more, when the researchers gave K. pneumoniae to mice that were genetically prone to developing colitis (inflammation of the colon), they found that K. pneumoniae persisted in the mice's intestines and caused severe inflammation.

These findings suggest that the K. pneumoniae strain can elicit "severe gut inflammation in the context of a genetically susceptible host," the researchers from the Keio University School of Medicine in Japan wrote in the Oct. 20 issue of the journal Science.

The researchers next analyzed information from a database of the human "fecal microbiome," which includes data on the types of bacterial DNA found in people's poop. They found that people with Crohn's disease and IBD had higher amounts of Klebsiella species in their poop, compared with healthy people.

The researchers hypothesize that, in people with IBD or other gut diseases, inflammation in the intestine may create an environment that is more hospitable to bacteria from the mouth. Once these oral bacteria (such as Klebsiella) colonize the gut, they may "help perpetuate gut microbiota dysbiosis [imbalance] and chronic inflammation," the researchers said.

"Thus, our findings indicate that targeting oral-derived bacteria, particularly Klebsiella, could provide a therapeutic strategy to correct IBD and many other disease conditions," the researchers wrote. One way to do this could be to identify "good bacteria" that could block Klebsiella from colonizing the gut, they said.

Original article on Live Science.

Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.